Many people use mobile stations, such as cell phones and personal digital assistants (PDAs), to communicate with cellular wireless networks. These mobile stations and networks typically communicate with each other over a radio frequency (RF) air interface according to a wireless communication protocol such as Code Division Multiple Access (CDMA), perhaps in conformance with one or more industry specifications such as IS-95 and IS-2000. Wireless networks that operate according to these specifications are often referred to as “1xRTT networks” (or “1x networks” for short), which stands for “Single Carrier Radio Transmission Technology.” These networks typically provide communication services such as voice, Short Message Service (SMS) messaging, and packet-data communication.
Mobile stations typically conduct these wireless communications with one or more base transceiver stations (BTSs), each of which send communications to and receive communications from mobile stations over the air interface. Each BTS is in turn communicatively connected with an entity known as a base station controller (BSC), which (a) controls one or more BTSs and (b) acts as a conduit between the BTS(s) and one or more switches or gateways, such as a mobile switching center (MSC) and/or packet data serving node (PDSN), which may in turn interface with one or more signaling and/or transport networks.
As such, mobile stations can typically communicate with one or more endpoints over the one or more signaling and/or transport networks from inside one or more coverage areas (such as cells and/or sectors) of one or more BTSs, via the BTS(s), a BSC, and an MSC and/or PDSN. In typical arrangements, MSCs interface with the public switched telephone network (PSTN), while PDSNs interface with one or more core packet-data networks and/or the Internet.
In some wireless communication systems or markets, a wireless service provider may implement more than one type of air interface protocol. For example, a carrier may support one or another version of CDMA, such as EIA/TIA/IS-2000 Rel. 0, A (hereafter “IS-2000”) for both circuit-cellular voice and data traffic, as well as a more exclusively packet-data-oriented protocol such as EIA/TIA/IS-856 Rel. 0, A, or other version thereof (hereafter “IS-856”). Mobile stations operating in such systems may be capable of communication with either or both protocols, and may further be capable of handing off between them, in addition to being able to hand off between various configurations of coverage areas.
In a further aspect, the RAN may be configured to engage in reverse-link power control with mobile station. In general, a base station may monitor indicators such as the frame error rate (FER), and periodically send the mobile station a power-control bit that indicates whether the mobile station should increase or decrease its transmit power. In an IS-2000 system, a base station typically sends a power-control bit sixteen times per frame.
Further, in an IS-2000 system, to control reverse-link transmission power and determine whether the power-control bit should provide a power-up or power-down instruction, the base station may use three different control loops. The first loop is referred to as the “open loop”, and is based on the level of power received in the total 1.25 MHz physical channel bandwidth. The second loop is referred to as the “closed” loop, and involves the base station measuring signal strength on the reverse traffic channels to determine if the reverse-link power at the desired level. Then, if reverse-link power is not at the desired level, the base station transmits a one-bit control message (i.e., a power-up or power-down message) to the mobile station at a rate of up to 800 bits/sec on the forward traffic channel. These power-up and power-down message typically adjust the mobile transmit power (i.e., reverse-link power) in steps of approximately 1 dB. The third loop is referred to as the “outer” loop, and involves the base station using reverse-link frame quality statistics (e.g., FER) to monitor the efficacy of the closed loop control. If the FER is above a desired level, the base station uses closed loop power control to instruct the mobile station to increase its transmit power (e.g., by transmitting a power-up message).